The invention relates to a rotating part of an electrically driven machine, a direct-current motor for a motor vehicle comprising such a rotating part and a method for making such a rotating part.
Direct-current motors for electric fans in motor vehicles are known which comprise an inductor with permanent magnets and a wire-wound armature. This armature has a support and a generally ring-shaped winding formed of strands wound around the support. The circulation of a current in the strands placed in the magnetic field generated by the inductor gives rise to a Laplace force in the strands which causes the rotation of the armature around its axis. The strands comprise rectilinear sections, parallel to the axis of the armature, and at the end thereof intermediate sections connected to the commutator or to another rectilinear section. The Laplace force essentially occurs only in the rectilinear sections.
The inactive intermediate sections are disposed and fitted together at the axial end faces of the winding to occupy a reduced space. These thus form bulges called armature leading-out wires. The spatial requirement of the leading-out wires in the axial direction of the motor is large, and may be equal to the length of the active rectilinear sections. The axial spatial requirement of the motor itself therefore depends to a great extent on the axial spatial requirement of the leading-out wires. In the motor industry, inter alia, there is today an increasing demand for motors having a reduced axial spatial requirement.
Moreover, the dimension of the winding in the axial direction, which is large, is matched with a tolerance range which is itself large. It follows that the parts of a motor adjacent to the winding occupy positions which take this tolerance range into consideration. The axial spatial requirement of the motor is therefore doubly increased.
Furthermore, the volumetric distribution of the strands parallel to the axes and of the leading-out wires is generally irregular. This poor distribution creates a weight imbalance or mass imbalance, which it is necessary to compensate by rebalancing the armature after production before mounting in the motor. This compensation forms an operation which becomes increasingly delicate as the initial lack of balance increases.
One problem is therefore of providing a method for producing a wire-wound rotating part having leading-out wires which have a reduced axial dimension and a reduced tolerance range associated with this dimension, and distributed more regularly than the leading-out wires of the above-mentioned rotating parts.
From the prior art, particularly the English translation of the abstract of the Japanese patent JP-4 275 050 (Fujitsu General Ltd), the production of a wound stator having a reduced axial dimension is known by winding the strands onto the sheet metal pack, then disposing the sheet metal pack with its winding in a press comprising two clamping jaws having opposite coaxial annular compression faces. The first clamping jaw has a core onto which the sheet metal pack with its winding is threaded. When the press is closed, the end of the core penetrates into a cavity of the second clamping jaw intended for this purpose. Then the two clamping jaws are brought closer to one another to perform the axial compression of the winding.
Thus, the compression force causes the crushing of the leading-out wires in the axial direction and brings about a great reduction in the axial spatial requirement of the winding.
However it is known that to produce the wire-wound rotating part of an electrically driven machine, it is advantageous to proceed as follows:
attach a bare sheet metal pack onto a shaft;
then fix a commutator onto the shaft in a temporary position spaced from the sheet metal pack;
then wind the strands simultaneously onto the sheet metal pack and the commutator; and finally
bring the commutator closer to the sheet metal pack to place it in its permanent position.
This method facilitates the production of the winding. The teaching of the abstract of the above-mentioned Japanese document cannot be used in these conditions, as it relates to a winding of a fixed part of an electrically driven machine which is provided with neither a shaft nor a commutator.
One object of the invention is to propose a method for producing a rotating part of an electrically driven machine enabling the winding to be produced simultaneously on the sheet metal pack and on the commutator in the temporary position before placing the commutator in the permanent position, whilst obtaining the above-mentioned advantages of the axial compression of the winding.
With a view to the achievement of this object, according to the invention there is specified a method for producing a wire-wound rotating part for an electrically driven machine, including stages consisting of:
attaching a sheet metal pack and a commutator onto a shaft, the commutator being spaced from the sheet metal pack; and
winding conductive strands onto the sheet metal pack and the commutator to form a generally ring-shaped winding,
the method also including the step consisting simultaneously of compressing the winding in an axial direction of the winding, and bringing the commutator closer to the sheet metal pack.
Thus, the temporary position of the commutator facilitates the production of the winding on the commutator and sheet metal pack. Moreover all the advantages of the axial compression of the winding are obtained. Furthermore, certain strands have an end connected to the commutator and another end connected to the axial end face of the winding directed towards the commutator. During the axial compression of the winding simultaneously with the displacement of the commutator, the two ends of these strands are displaced in the same direction in the axial direction of the shaft. Consequently, between these two ends no traction occurs which is likely to alter or break the strand, and the excess of strands adjacent to the commutator does not produce any masses from which short circuits could result. The risk of contact, or shocks, between the strands is reduced. This method generally enables the deterioration of the insulating sheath or of the insulating varnish of the strands to be avoided to a great extent during compression, which deterioration could in the opposite case cause short circuits between the strands. In particular, the crushing of the strands which could cause the cutting of some of them is avoided.
The method advantageously includes during compression the phase consisting of guiding strand sections extending from the commutator to the sheet metal pack.
Thus the above-mentioned drawbacks are further avoided, for the strands adjacent to the commutator, i.e. the formation of masses, their crushing or their excessive traction, from which a contrario the alteration of the insulating material of the strands and short circuits between them could result.
The guiding phase advantageously includes the operation consisting of keeping each of the said strand sections in a fixed radial plane determined in relation to the shaft.
It involves a particularly simple manner of producing this guidance.
Conductive strands having an outer sheath made of thermosetting material are advantageously wound onto the support, and during the compression stage the winding is heated to a temperature at least equal to the setting temperature of this material.
Thus the strands are immobilised in the compression position of the winding. Therefore the service life of the obtained arrangement of the strands is prolonged.
The winding is advantageously heated by circulating electric current in the strands.
Thus it is not necessary to use a press equipped with its own heating means.
Before the compression stage, a hot liquid substance which can harden on cooling is advantageously applied onto the strands, and the compression stage is extended until the cooling of the substance.
It involves another manner of obtaining the immobilisation of the strands in the compressed position.
The invention also relates to a press for the production of a wire-wound rotating part for an electrically driven machine, the press comprising a first clamping jaw and a second clamping jaw having respective compression faces having a general ring-shape in plan view, coaxial to one another and extending opposite one another, the press being designed to move the two clamping jaws relatively in the axial direction of the compression faces, each clamping jaw having a cavity in the centre of the compression face, with at least the first clamping jaw having a generally ring-shaped bearing face in plan view, coaxial to the compression face, having a larger diameter which is less than a smaller diameter of the compression face, and forming a base of the cavity.
This press enables the method according to the invention to be used. This press may ensure in particular the compression of the winding by the direct contact of the compression faces with the axial end faces of the winding.
The cavity having the bearing face may receive the commutator, the bearing face stressing the commutator for its displacement from its temporary position to its permanent position.
The second clamping jaw advantageously has a generally ring-shaped bearing face, coaxial to the compression face, having a larger diameter which is less than that of the bearing face of the first clamping jaw and forming a base of the cavity associated with the second clamping jaw.
This cavity may receive the end of the shaft opposite the commutator. Thus, the displacement of the commutator is performed by stressing the commutator, on the one hand, and the axial end of the shaft opposite the commutator, on the other hand, towards one other in the axial direction. For the displacement of the commutator it is therefore not necessary to further stress the axial end face of the winding opposite the commutator.
At least one of the clamping jaws advantageously has at least one contoured edge which is ring-shaped in top view, prolonging the compression face and protruding therefrom towards the other clamping jaw, the edge having a contour like the sector of an ellipse or of a parabola, the compression face having a rectilinear contour touching a vertex of the ellipse or of the parabola.
During compression, this edge ensures the guidance of the peripheral strands adjacent to the axial end faces of the sheet metal pack. The ellipse-shaped or parabola-shaped contour enables this guidance to be performed by reducing as far as possible the risks of crushing the strands.
The edge is advantageously prolonged by another curved contour, the junction between the two contours forming a point of inflection.
Thus, one can avoid producing a protruding edge at the end of the guide contour.
The press advantageously comprises stop means designed to limit the relative displacement of the clamping jaws towards one another to prevent the relative moving together of the compression faces within a predetermined distance.
Thus any excessive compression of the winding is prevented, from which an irreversible alteration of the strands could result.
The stop means advantageously comprise plane stop faces on the clamping jaws, roughly perpendicular to the axis, and designed to come into contact with one another.
The press advantageously comprises at least one series of bulges designed to be disposed in the vicinity of the cavity and protruding from a plane of the compression face of the first clamping jaw towards the second clamping jaw, the bulges being disposed roughly in a circle coaxial to the cavity, regularly around the axis.
Thus during compression these bulges ensure the guidance of the strands connected to the commutator which was involved above.
The bulges are advantageously borne by the first clamping jaw.
The press advantageously comprises a slide which can move by sliding through the first clamping jaw in relation thereto, in the axial direction, the slide bearing the bulges.
Thus the position of the bulges may be changed at will (for example to make the bulges protrude more or less) during the various compression phases and/or as a function of the configuration of the produced rotating part.
At the least the compression faces are produced from steel, these faces having undergone a superficial treatment such as case hardening, nitride hardening or carbonitriding.
In fact it is advantageous for the clamping jaws to have a certain superficial hardness, for example 55 to 60 HRC (Rockwell) and also good sliding properties, and also a good surface state, to avoid harming the strands during the compression.
Furthermore according to the invention there is specified a wire-wound rotating part for an electrically driven machine which was produced by means of the method specified by the invention.
Furthermore according to the invention there is specified a wire-wound rotating part for an electrically driven machine, comprising a shaft, a sheet metal pack and a commutator attached to the shaft, and a generally ring-shaped winding comprising conductive strands wound onto the sheet metal pack and commutator, the rotating part comprising at least one series of elongated pins disposed in a circle coaxial to the shaft regularly around the shaft, the pins being oriented in a direction roughly opposite to the sheet metal pack and being designed to be interposed radially between the commutator and the winding.
Thus, guide bulges of the strands adjacent to the commutator are borne by the rotating part itself, as a replacement or as a supplement to those borne by the press.
The rotating part advantageously comprises a washer threaded onto the shaft and bearing the pins.
The washer may more particularly be placed in the axial direction between the commutator and the winding, and even attached to the commutator.
The rotating part advantageously comprises an insulating plate integrated in the sheet metal pack parallel thereto and bearing the pins.
The plate may be the insulating cheek or star disposed, as is known, at each end of the sheet metal pack before the production of the winding.
The strands are advantageously glued to one another by means of a material applied to the strands.
It advantageously relates to a direct-current motor armature for a motor vehicle.
It advantageously relates to an armature for an electric fan.
Furthermore in accordance with the invention a direct-current motor for a motor vehicle comprising a rotating part as specified by the invention is specified.